The present invention relates to a radio reception apparatus and a method for detecting reception timing, both being used in a digital radio communication system.
A propagation path in a digital radio communication system has a frequency characteristic as a transmission path, and then the propagation path has a transmission characteristic having selectivity to frequencies, since the propagation path is generally composed of multipath. Moreover, these characteristics vary with time as a communication terminal such as a mobile station moves, and a received signal consequently has fading different in its frequency band. The fading is called as selective fading.
As a measure against the selective fading, there is an adaptive array technique. The adaptive array technique is a technique in which a plurality of antenna elements are prepared and signals received by these antenna elements are weighted to be combined.
In such an adaptive array technique, reception timing is detected for receiving a desired signal correctly. An adaptive array antenna device having a reception timing detection function as a conventional radio reception apparatus is disclosed in Japanese laid-open patent publication HEI 10-51221. FIG. 1 is a block diagram showing the schematic configuration of the adaptive array antenna device.
The adaptive array antenna device outputs signals received by antennas 1-1 to 1-n to weighting circuits 2-1 to 2-n, respectively. The weighting circuits 2-1 to 2-n weight each of the signals for controlling directivity, and output the weighted signals to a combining circuit 3 for combining the weighed signals.
The combined signal is output to a receiver 4 and a frame synchronization circuit 6. The receiver 4 demodulates the combined signal to output a demodulated output. Moreover, the receiver 4 detects the received signal strength indicator (RSSI) of the combined signal to output the detected result (RSSI signal) to a weighting controller 7.
Furthermore, the frame synchronization circuit 6 maintains the synchronization on the basis of the combined signal, and outputs the synchronization timing to the weighting controller 7. The weighting controller 7 controls respective weighting coefficients for outputting them to the weighting circuits 2-1 to 2-n so as to maintain the timing that the RSSI signal takes its maximum. The weighting coefficients are fittingly stored in a memory 8.
However, in the conventional adaptive array antenna device, a delay profile shown in FIG. 2 is generated. That is, if the device receives signals without isolating directivities in the case where a desired station and an interference station exist, signals from the desired station are received at the times xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d. The signal at the time xe2x80x9caxe2x80x9d is a signal that arrives the device directly from a direction xe2x80x9cBxe2x80x9d. The signal at the time xe2x80x9cbxe2x80x9d is a signal that arrives the device from a direction xe2x80x9cAxe2x80x9d after being reflected by a far reflecting object such as a mountain. (See FIG. 5 about the directions xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d.) Consequently, the signal at the time xe2x80x9cbxe2x80x9d arrives the device later than the signal at the time xe2x80x9caxe2x80x9d. In this case, because signals from directions except for the direction of the desired station all become interference signals, there exist many interference signals in the case where the directivity is not isolated. When many interference signals exist, it becomes difficult to detect reception timing correctly.
Moreover, in the case where the directivity is not isolated, signals arrived from directions other than the directivity formed by the weighting circuits 2-1 to 2-n cannot be received. Furthermore, at the time of turning on its power or in case of detecting signals received from all directions, the weighting control takes very long time.
An object of the present invention is to provide a radio reception apparatus and a reception timing detection circuit, both capable of detecting the reception timing precisely at the time of detecting signals received from all directions such as a time when its power supply is turned on, and besides at the time of receiving a signal arrived from a direction different from a currently receiving direction during performing communication.
The inventor of the present invention paid attention to the fact that all the signals from directions except for the direction, to which the directivity was generated, became interference signals when directivity reception was performed, and the fact that the interference signals made the precise detection of the reception timing difficult. And the inventor found that the interference amount in each directivity could be decreased by dispersing the interference signals by providing a plurality of fixed directivities. Consequently, those facts led the present invention.
That is, the subject matter of the present invention is to narrow down directions from which interference signals reach by means of delay profiles generated for each fixed directivity to suppress the interference amount of the interference signals for performing the detection of reception timing or the selection of a path.